Our proposed research will investigate the mechanisms involved in construction of an internal model of space by imposing a gross distortion on incoming visuospatial information and observing various areas of the brain for signs of adaptive plastic reorganization. For two weeks, subjects will wear an apparatus that inverts the visual world. Previous studies have shown that subjects exposed to chronically inverted vision undergo a remarkable adaptation, after which they are able to interact normally with the external world. During our research, the subjects will be observed intensively with functional MRI and behavioral testing. Areas studied will include striate and extrastriate occipital cortex, the superior and inferior colliculi, posterior parietal cortex, and superior temporal cortex. We will obtain detailed maps of the functional organization of these areas prior to inversion, repeatedly during adaptation to inverted vision, and after removal of the inverting device; we will pay special attention to changes in the spatiotopic organization of these areas. This work is designed to identify the site of the neural plasticity that permits adaptation to inverted vision. Plastic changes of the human brain are the essential process by which we recover from injuries such as stroke. Further, the physical plasticity of the human brain can be exploited in the development of training regimens to overcome such debilitating conditions as dyslexia, and following traumatic spinal transection. In adults, there remains sufficient capacity for local reorganization that individuals with severe brain or spinal damage can recover the ability to walk. In spite of the overwhelming clinical significance of the phenomena, little is yet known of the extent to which plastic changes can occur. Knowledge of the nature of plasticity in areas of the brain specifically concerned with external space may help in understanding conditions such as hemispatial neglect syndrome, in which damage to the parietal cortex causes an inability to perceive the left side of external space, and blindsight, in which subjects who lack conscious visual perception can still react to visual stimuli. Such knowledge will also be valuable in preparing humans for space travel, when people must adapt to the loss of gravitational clues to spatial orientation.